Acoustic coupler

ABSTRACT

An acoustic coupler for coupling a telephone handset to a source of shift frequency signals representing binary information comprising an enclosure adapted to mount a handset on edge so that the microphone of the handset is oriented in a vertical position. The coupler&#39;&#39;s speaker, having a cone with a mouth portion, is tightly sealed within a housing with the mouth portion of the speaker cone in communication with an opening in the housing and the housing is sealed within the enclosure. The mouth portion of the speaker cone is also directly opposite and axially withdrawn from an exit portion in the enclosure so that there is a passage between the mouth of the speaker cone and the interior of the enclosure. The area of the exit port is slightly smaller than the area of the mouth portion of the speaker cone, and the peripheral edge of the exit port is surrounded by a collar of elastomeric material to acoustically and sealingly engage the transmitter portion of the telephone handset. An acoustic energy absorbing material such as felt covers the mouth portion of the speaker cone to provide an acoustic low-pass filter and the walls of the enclosure to provide high audio frequency damping.

United States Patent 11113,553,374

{721 Inventors Edearwolf 2,529,228 11/1950 Schwalm 179/180 N Hy3,116,376 12/1963 Behymeretal..... 179/107 s m z m 3,299,207 1/1967Cooke 179/](C) 1211 AppL O- 808,979 1 3,319,003 5/1967 Prager 179/1 c)[22] Filed Mar-20.1969 3,360,071 12/1967 Vogelman 181/05Continuation-impart of Ser. No. 628,847, Aug. 17, 1967, now abandoned,which is a continuation-in-part of Ser. No. 482,340, Aug. 25, 1965. nowabandoned.

[] Patented Ian. 5, 1971 [73] Assignee DigitronicsCorporationAlbertsomN-Y. a corporation of Delaware [54] ACOUSTIC COUPLER I PrimaryExaminer-Kath1een Claffy Assistant Examiner-Charles W. JirauchAttorney-Yuter and Fields oriented in a vertical position. The couplersspeaker, having a cone with a mouth portion, is tightly sealed within ahousing 6 Claims, 2 Drawing Figs. 5 2 U s m w1th the mouth port1on ofthe speaker cone 1n commumcatlon 1 179/1 with an opening in the housingand the housing is sealed within c 179/2 the enclosure. The mouthportion of the speaker cone is also [51] I H28 directly opposite andaxially withdrawn from an eigit port in Field ofSearcli 179/1C, 2C, theenclosure so that there is a passage between the mouth f l8 the speakercone and the interior of the enclosure. The area of the exit port isslightly smaller than the area of the mouth por- [56] References Citedtion of the speaker cone, and the peripheral edge of the exit UNITEDSTATES PATENTS port is surrounded by a collar of elastomeric material to,463 11/1954 Robbins et a1- /31(1) acoustically and sealingly engage thetransmitter portion of 3, 6 L ll /3l(-l) the telephone handset. Anacoustic energy absorbing material 3,146,848 9/ 1964 Fundlngsland18l/3l( .1) such as felt covers the mouth portion of the speaker cone to3.194.340 7/1965 Kuwayama l provide an acoustic low-pass filter and thewalls of the enclo- 2,506,279 5/1950 Rowe l79/2(C) sure to provide highaudio frequency damping.

o K 19. 1 2e0- sec 16 I 1. 23C 2 .1 265 I l '1 3013 I I '1 38B ass 1 I38A 338 Ill. 15

17 11 2e 42 I 30 34 32 36A 36B 1 l 'I' I I g I PATENTEUJAN 5m! 3553374INVENTORS Ed gar Wolf BY Francis C. Marino ATTORNEYS ACOUSTIC COUPLERThis application is a continuation-in-part of copending application Ser.No. 662,847, filed Aug. 17, 1967 now abancloned which, in turn, was acontinuation-in-part of application Ser. No. 482,340, filed Aug. 25,1965 now abandoned, both of said applications being entitled AcousticCoupler."

This invention pertains to the acoustic coupling of tones to a signaltransmitter and more particularly to the coupling of tones from a sourceof binary information represented by shift frequency signals to acommunication link.

In the data processing and communication fields there are many instanceswhere information from a remote source must be transmitted to a centralprocessing location. Heretofore, special purpose communication linkshave been utilized. However, because of the expense in building andmaintaining such links these systems can be exploited only by mostaffluent users. Lately there have been proposals to utilize publicutility telephone systems as the communication link between a remotesource and a central processor. In fact, special purpose equipment isavailable from the telephone utilities to provide the input and outputterminals of the system. Nevertheless, such equipment is still tooexpensive for many potential users.

It is possible to devise a very inexpensive input device comprising afrequency shift keying tone generator which generates audio tones thatbinarily represent the information to be transmitted. In theory, it isonly necessary to feed the audio tones into the transmitter portion ofthe handset of a conventional subscriber telephone connected into apublic utility telephone system. At the output, a microphone ispositioned against the receiver portion of a handset and the receivedtones are converted to binary information signals.

However, in practice, it is difficult to obtain reliable transmission.One of the major sources of unreliability comes from introducing thetones into the transmitter portion of a handset. Frequency shiftrepresentation of information utilizes a first frequency tone torepresent a mark and a second frequency tone to represent a space. Inorder to maximize transmission rate, one frequency is typically roughlytwice the other frequency. In the course of transmitting the informationthe tone abruptly shifts between the frequencies. Such abrupt shiftsrequire that the transducer or coupler have excellent transient andfrequency response and reasonably good sinusoidal output waveforms. Inparticular, there should be a minimum of phase shift and harmonicdistortion. For example, it should be noted that any second harmonicdistortion in the lower frequency tone would tend to look like thehigher frequency tone to the handset transmitter.

Another source of unreliability is due to the fact that considerablesecond harmonic distortion and significant loss in amplitude arise whenthe handset is mounted on the transducer in the horizontal position(i.e., that position which the handset normally occupies on thetelephone base). This distortion and amplitude loss may be'attributed tosettling of the carbon granules used in the microphone (or granularcarbon transmitter") of the handset. The effect, which shows up when themicrophone is left in the horizontal position for long periods,increases the likelihood of error in the transmitted informationsignals. Thus a transducer or a coupler should preferably mount thehandset in a position such that the harmonic distortion due tomicrophone granule settling is substantially eliminated.

Furthermore, in order to eliminate ambient noise the transducer orcoupler should be in intimate acoustic contact with the handsettransmitter. Ideally, the transducer should be fitted over thetransmitter portion of the handset with a minimum of air leakage.However, subscriber telephones use many different varieties oftransmitters. For example, the Western Electric Company manufactures atleast three types of Granular Carbon Transmitter, i.e.', Types Tl, F1and T2. Other manufacturers use Fl sizes and shapes of transmitters.Therefore, as a practical matter a coupler must have a universalapplicability. Otherwise, a special coupler would be necessary for eachtype of transmitter.

In addition, the input side of the transmitter, i.e., the mouthpieceportion of the handset causes reflections of the acoustic waves back tothe coupler. These reflections cause distortions in the acoustic signalsemitted by the coupler. While voice communication between human beingscan tolerate these distortions, digital communication cannot.

Another consideration to be taken into account includes the bassresonant frequency of the loud speaker. More particularly, it is highlyundesirable to have a loudspeaker construction with a high bass resonantfrequency in view of the fact that one frequency in presently usedfrequency shift keying systems is relatively low.

It is, accordingly, a general object of the invention to pro vide animproved binary tone coupler for transmitting shift frequency tones to atelephone transmitter It is another object of the invention to providesuch a coupler which has good transient and frequency response andintroduces a minimum of harmonic distortion in the tones.

Another object of the invention is the provision of a coupler whichmounts a handset in such a manner so to substantially eliminate thegeneration of harmonic distortion and amplitude reduction.

It is a further object of the invention to provide a coupler for usewith a great variety of types, sizes and shapes of telephonetransmitters employed in the handsets of public utility subscribertelephones.

Briefly, the invention contemplates a transducer comprising a housingwhich is provided with an opening. A speaker is positioned in thehousing. The speaker has a speaker cone with a mouth portion positionedin the opening of the housing. A member of material which partiallyabsorbs acoustic energy completely covers the mouth portion of thespeaker cone to provide an acoustic filter. Accordingly, when thetransducer is fitted against the transmitter portion of a telephonehandset? good transient and frequency response is obtained.

Other features and advantages of the present invention will become moreapparent from a consideration of the following detailed description whentaken in conjunction with the accompanying drawings, in which: FIG. 1 isa front elevational view of an acoustic coupler constructed according tothe present invention; and

FIG. 2 is a partial sectional view thereof, taken along the line 24 ofFIG. 1.

Referring now to FIG. 1, the coupler 10 includes an enclosure 11 havinga bottom wall 12, rear wall 13, opposed sidewalls l5 and 17, a top wall21, and a front wall 19 which is provided with two exit ports 14 and 16.Surrounding exit ports 14 and 16 are collars l8 and 20, respectively.When a telephone handset is rested in the coupler, the transmitterportion is received within collar 20 and the receiver portion isreceived within collar 18. The collars are made of an elastomer such assoft rubber to assist in proper positioning of the many differentlysized handsets to the coupler and to minimize leakage of ambient soundsin the system.

A member in the form of disc 22 completely covers exit port 16. Themember 22 may be made of felt or some other rnateri al havingsoundabsorbent characteristics. This member serves to eliminate standingwaves between a speaker or an output transducer 28 and the hard plasticcover of the telephone handsets transmitter. Additionally, the member 22functions as an acoustical low-pass filter thereby to eliminate most ofthe undesirable higher frequency harmonics.

Bushinglike spacers 26A and 268 support output transducer 28 in spacedrelationship to the wall of the enclosure 11. Similarly bushinglikespacers 26C and 26D support input transducer 30 in spaced relationshipto the wall of enclosure 11. The spacing is best seen with respect totransducer 30.

The output transducer 28 includes the cup shaped housing 32 of a dense,rigid material such as aluminum. Within the housing 32 are a felt basedisc 34, and a plurality of felt washers 36A36C. Fitted in the housingand cushioned by the disc 34 and washers 36 is a speaker 38 including apermanent magnet 38A, a speaker cone 38C and a voice coil (not shown)which is energized by leads 38. The speaker cone 38C is in the open endof housing 32 and the mouth of speaker cone 38 faces exit port 16. Theflange 38E of speaker cone 38C is supported between felt washer 40 andspacers 26A, 26B. Screws (not shown) start from the wall of enclosure11, pass through spacers 26A, 26B flange 38E and washer 40 and terminatein threaded openings in the wall of housing 32.

It should be noted that by virtue of flange 38B and washer 40, housing32 is completely sealed to prevent the escape of any acoustic backwaves.In addition, by virtue of spacers 26A, 268 there is an air passagewaybetween the mouth of speaker cone 38C and the interior of enclosure 11which is lined with sound-absorbing material 42. Such a passageway makesthe coupling between the speaker and the handset transmitter equivalentto a transformer with a low k. Thus, the coupling is improved and thelow frequency response is controlled.

In an enclosure of the type under consideration, the bass frequencyresponse of the transducer increases with decreasing volume. To reduceany upward shift of the bass resonant frequency and to effect adequateacoustical damping, the area of the exit port 16 is made to be slightlysmaller than the area of the mouth of the speaker cone. 38C.Additionally, the I sound-absorbent material 42, which may be felt orthe like, serves to dampen or eliminate standing waves in the higheraudio frequency-range while having little effect on the lowerfrequencies. That is, all the material lies within a small fraction of awavelength of the inner wall, which is effecting a velocity node, sothere is no motion of the air particles at the boundary of theacoustical material. Thus, the combination acts as an acoustic couplerhaving a controlled passband.

The input transducer portion is similar to the above described outputtransducer portion except that a further felt washer 44 is provided tominimize acoustic communication from the mouth of the speaker cone andthe interior of enclosure 12.

There has thus been shown an improved coupler which, b utilizing amember of material which partially absorbs acoustic energy across theexit port of an enclosure adjacent to the mouth of a speaker cone,provides good transient and frequency response and minimizes harmonicdistortion because the member acts as a low-pass filter. In addition, byproviding in such a combination an air passageway between the mouth ofthe speaker cone and the interior of the enclosure and by properlydimensioning the exit port, the low frequency response of the coupler iscontrolled so that the coupler in effect includes a band-pass filter.

It will also be appreciated that the coupler l0 mounts the microphone ofa handset in a vertical position rather than the conventional horizontalposition thereby to substantially reduce the generation of harmonicdistortion and minimize amplitude reduction which would otherwise ariseif the handset were oriented in the horizontal position for long periodsof time. To be more specific, it has been found that second harmonicdistortion of signals is substantially eliminated when the handset isplaced with the microphone or transmitter in a vertical position ratherthan a horizontal position. Accordingly, when the coupler of the presentinvention is utilized in the manner described above, with thebottom-wall 12 resting on a supporting surface, the handset will bepositioned on edge. Hence, the microphone will be oriented in a verticalplane to reduce the aforementioned distortion.

While only one embodiment of the invention has been shown and describedin detail, there will now be obvious to those skilled in the art manymodifications and variations which satisfy many or all of the objects ofthe invention but which do not depart from the spirit thereof as definedin the appended claims.

We claim:

1. A transducer for use with a telephone handset and the like comprisinga housing, said housing being provided with an opening, a speakerpositioned in said housing, said speaker ineluding a speaker cone with amouth portion positioned in the opening of said housing, and a low-passfilter means com letely covering the mouth portion of said speaker cone,sai lowpass filter means comprising a felt disc, said transducer furtherincluding sealing means for sealing said speaker in said housing so thatonly the mouth portion of said speaker cone can communicate with theregion external to said housing, an enclosure provided with an exitportenclosing said housing and said speaker with the mouth portion of saidspeaker cone directly opposite the exit port, said sealing meansincluding spacing means for supporting said speaker so that the mouthportion of the speaker cone is within said enclosure and axiallywithdrawn from said exit port, and a passage between the mouth of thespeaker and the interior of the enclosure to control low frequencyresponse of said speaker.

2. A transducer as in claim 1, in which said sealing means furtherincludes a washer of acoustically-absorbing material between saidhousing and said speaker cone.

3. A transducer for coupling tones to the transmitter portion of atelephone handset comprising a housing provided with an opening, aspeaker including a speaker cone having a mouth portion, said speakerbeing disposed in said housing with the mouth portion of said speakercone being disposed in said opening, means for tightly sealing saidspeaker in said housing so that only the mouth portion of said speakercone can communicate with the region external to said housing, anenclosure provided with an exit port, said housing and said speakerbeing disposed in said enclosure with the mouth portion of said speakercone directly opposite the exit port, and a collar of elastomericmaterial around the peripheral edge of the exit port for acousticallysealingly engaging the transmitter portion of the telephone handset, thearea of said exit port being slightly smaller than the area of the mouthof said speaker, said transducer further including means for supportingsaid housing and said speaker so that the mouth portion of the speakercone is within said enclosure and axially withdrawn from the exit port,and a passage between the mouth of the speaker and the interior of theenclosure to control low frequency response of said speaker.

4. A transducer as in claim 3, in which said enclosure includes a bottomwall, a top wall, opposed sidewalls, a front wall, and a rear wall; saidexit port being provided in said front wall, whereby a telephone handsetis oriented with the granular carbon transmitter in a vertical positionwhen connected with said transducer.

5. A transducer as in claim 3, and high audio frequency damping meansdisposed on the interior wall portions of said enclosure.

6. A transducer for coupling tones to the transmitter portion of atelephone handset comprising a housing provided with an opening, aspeaker including a speaker cone having a mouth portion, said speakerbeing disposed in said housing with the mouth portion of 'said speakercone being disposed in said opening, means for sealing said speaker insaid housing so that only the mouth portion of said speaker cone cancommunicate with the region external to said housing, and enclosureprovided with an exit port, said housing and said speaker being disposedin said enclosure with the mouth portion of said speaker cone directlyopposite the exit port, a member of material which partially absorbsacoustic energy completely covering said exit port to provide andacoustic filter, a collar of elastomeric material around the peripheraledge of the exit port for acoustically sealingly engaging thetransmitter portion of the telephone handset, means for supporting saidhousing and said speaker so that the mouth portion of the speaker coneis within said enclosure and axially withdrawn from the exit port andthe face of said housing is spaced from the interior side of the walldefining said exit port, and acoustic energy absorbing means disposed onthe interior wall portions of said enclosure. 1

Patent No. 3,553,374 Dated January 5, 1971 Edgar Wolf et a1 Inventor(s)It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the cover sheet the illustrative drawing and FIG. 2, the referencecharacter "38B", each occurrence, should read 38 Column 3, line 1, "38"should read 38D line "38" should read 38C Column 4, line 56, "and"should re an line 61 "and" should read an Signed and sealed this 16thday of May 1972 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A transducer for use with a telephone handset and the like comprisinga housing, said housing being provided with an opening, a speakerpositioned in said housing, said speaker including a speaker cone with amouth portion positioned in the opening of said housing, and a low-passfilter means completely covering the mouth portion of said speaker cone,said low-pass filter means comprising a felt disc, said transducerfurther including sealing means for sealing said speaker in said housingso that only the mouth portion of said speaker cone can communicate withthe region external to said housing, an enclosure provided with an exitport enclosing said housing and said speaker with the mouth portion ofsaid speaker cone directly opposite the exit port, said sealing meansincluding spacing means for supporting said speaker so that the mouthportion of the speaker cone is within said enclosure and axiallywithdrawn from said exit port, and a passage between the mouth of thespeaker and the interior of the enclosure to control low frequencyresponse of said speaker.
 2. A transducer as in claim 1, in which saidsealing means further includes a washer of acoustically-absorbingmaterial between said housing and said speaker cone.
 3. A transducer forcoupling tones to the transmitter portion of a telephone handsetcomprising a housing provided with an opening, a speaker including aspeaker cone having a mouth portion, said speaker being disposed in saidhousing with thE mouth portion of said speaker cone being disposed insaid opening, means for tightly sealing said speaker in said housing sothat only the mouth portion of said speaker cone can communicate withthe region external to said housing, an enclosure provided with an exitport, said housing and said speaker being disposed in said enclosurewith the mouth portion of said speaker cone directly opposite the exitport, and a collar of elastomeric material around the peripheral edge ofthe exit port for acoustically sealingly engaging the transmitterportion of the telephone handset, the area of said exit port beingslightly smaller than the area of the mouth of said speaker, saidtransducer further including means for supporting said housing and saidspeaker so that the mouth portion of the speaker cone is within saidenclosure and axially withdrawn from the exit port, and a passagebetween the mouth of the speaker and the interior of the enclosure tocontrol low frequency response of said speaker.
 4. A transducer as inclaim 3, in which said enclosure includes a bottom wall, a top wall,opposed sidewalls, a front wall, and a rear wall; said exit port beingprovided in said front wall, whereby a telephone handset is orientedwith the granular carbon transmitter in a vertical position whenconnected with said transducer.
 5. A transducer as in claim 3, and highaudio frequency damping means disposed on the interior wall portions ofsaid enclosure.
 6. A transducer for coupling tones to the transmitterportion of a telephone handset comprising a housing provided with anopening, a speaker including a speaker cone having a mouth portion, saidspeaker being disposed in said housing with the mouth portion of saidspeaker cone being disposed in said opening, means for sealing saidspeaker in said housing so that only the mouth portion of said speakercone can communicate with the region external to said housing, andenclosure provided with an exit port, said housing and said speakerbeing disposed in said enclosure with the mouth portion of said speakercone directly opposite the exit port, a member of material whichpartially absorbs acoustic energy completely covering said exit port toprovide and acoustic filter, a collar of elastomeric material around theperipheral edge of the exit port for acoustically sealingly engaging thetransmitter portion of the telephone handset, means for supporting saidhousing and said speaker so that the mouth portion of the speaker coneis within said enclosure and axially withdrawn from the exit port andthe face of said housing is spaced from the interior side of the walldefining said exit port, and acoustic energy absorbing means disposed onthe interior wall portions of said enclosure.